Bottom trawling not only impacts the seafloor but also changes the ambient water quality due to the disturbance of nutrients and sediment settled on the seafloor.
The severity and longevity of trawling impacts depends on factors such as depth, substrate, fishing intensity (i.e., the frequency of trawling), natural disturbance regime, and the life histories of the species being impacted.
Trawling over their habitat causes immense damage to both the habitat and the species assemblages.
Although trawl nets were used by sailing vessels up to the 19th century, it was only with the development of steam power and the diesel engine that bottom trawling became a widely used method of fishing.
The net is held open vertically on an otter trawl by floats and/or kites attached to the "headline" (the rope which runs along the upper mouth of the net), and weighted "bobbins" attached to the "foot rope" (the rope which runs along the lower mouth of the net).
The speed that the trawl is towed at depends on the swimming speed of the species which is being targeted and the exact gear that is being used, but for most demersal species, a speed of around 4 knots (7 km/h) is appropriate.
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